Programming Multistage Shape Memory and Variable Recovery Force with 4D Printing Parameters

Multistage shape changing is essential for soft robots and actuators, which is difficult to achieve via current 4D printing methods. While 4D printing smart materials and structures are widely investigated, the effect of 3D printing parameters on 4D behaviors, on the other hand, is not adequately explored thus far. Here, it is proposed to program multistage shape memory and variable recovery force by designing 4D printing parameters. Specifically, the effects of nozzle temperature, layer thickness, geometric thickness, and filling angle on shape memory properties of polylactic acid are investigated. It is found that the nozzle temperature apparently affects shape recovery time, and the filling angle apparently affects shape recovery force. Further, the geometric thickness of specimens simultaneously affects recovery time and force. Based on the relationship between shape memory properties and process parameters, the programming of shape recovery speed and recovery force is achieved successfully. As a proof-of-concept, an order of the shape recovery of artificial fingers and a lifting box that can use shape recovery force to lift different weights are demonstrated. This strategy fully takes the advantages of 4D printing technology and enriches the approach to the control of 4D printing actuators and soft robots.